Basic Science Research
Division of Nephrology faculty are actively involved in both basic and clinical research. Within the KRC facilities, Dr. Hallows is studying the metabolic control of kidney epithelial salt and water transport mechanisms with relevance to hypertension, acute kidney injury and chronic kidney disease. He is also studying the role of metabolic changes in autosomal dominant polycystic kidney disease at various levels: (1) the molecular and cellular level using in vitro model systems and electrophysiological, molecular genetic, biochemical, and imaging techniques; (2) animal disease models using in vivo imaging and functional studies (e.g., of metabolism, metabolomics and proteomics); and (3) patient samples (analysis of urine to identify and evaluate novel biomarkers that inform on disease severity, prognosis and response to new therapies). Dr. Pastor-Soler is studying the molecular and cellular mechanisms by which metabolic pathways in the kidney are affected by acidosis, a known predictor of CKD progression. She is also studying renal cell carcinomas with the aim to confirm a novel biomarker that could be used clinically to assess the presence and severity of this disease. Dr. Campese has been studying the role of the sympathetic nervous system in hypertension associated with kidney disease as well as essential hypertension. He is also involved in studying the role of renal denervation or baroreceptor stimulation in patients with resistant hypertension. Other faculty have a variety of clinical protocols dealing with diabetic nephropathy, bone disease, progression of kidney disease, kidney transplantation, vitamin deficiency in chronic kidney disease, end-stage renal disease, transplantation and nutrition in patients with acute kidney injury.
Special Basic Research Activities
Al-bataineh, MM, Alzamora, R, Marciszyn, AL, Li, H, Gong, F, Hallows, KR, and Pastor-Soler, NM. Aurora kinase A activates the vacuolar H+-ATPase (V-ATPase) in kidney cancer cells. Am. J. Physiol. Renal Physiol. 310: F1216-F1228, 2016.
Extracellular proton-secreting transport systems that contribute to extracellular pH include the vacuolar H(+)-ATPase (V-ATPase). This pump, which mediates ATP-driven transport of H(+) across membranes, is involved in metastasis. We previously showed that V-ATPase A subunit phosphorylation at Ser-175 is important for PKA-induced V-ATPase activity at the membrane of kidney intercalated cells. However, Ser-175 is also located within a larger phosphorylation consensus sequence for Aurora kinases, which are known to phosphorylate proteins that contribute to the pathogenesis of metastatic carcinomas. We thus hypothesized that Aurora kinase A (AURKA), overexpressed in aggressive carcinomas, regulates the V-ATPase in human kidney carcinoma cells (Caki-2) via Ser-175 phosphorylation. We found that AURKA is abnormally expressed in Caki-2 cells, where it binds the V-ATPase A subunit in an AURKA phosphorylation-dependent manner. Treatment with the AURKA activator anacardic acid increased V-ATPase expression and activity at the plasma membrane of Caki-2 cells. In addition, AURKA phosphorylates the V-ATPase A subunit at Ser-175 in vitro and in Caki-2 cells. Immunolabeling revealed that anacardic acid induced marked membrane accumulation of the V-ATPase A subunit in transfected Caki-2 cells. However, anacardic acid failed to induce membrane accumulation of a phosphorylation-deficient Ser-175-to-Ala (S175A) A subunit mutant. Finally, S175A-expressing cells had decreased migration in a wound-healing assay compared with cells expressing wild-type or a phospho-mimetic Ser-175-to-Asp (S175D) mutant A subunit. We conclude that AURKA activates the V-ATPase in kidney carcinoma cells via phosphorylation of Ser-175 in the V-ATPase A subunit. This regulation contributes to kidney carcinoma V-ATPase-mediated extracellular acidification and cell migration.
Roy A, Al-Qusairi L, Donnelly BF, Ronzaud C, Marciszyn AL, Gong F, Chang YP, Butterworth MB, Pastor-Soler NM, Hallows KR, Staub O, Subramanya AR: Alternatively spliced proline-rich cassettes link WNK1 to aldosterone action. J Clin Invest 125: 3433-3348, 2015.The thiazide-sensitive NaCl cotransporter (NCC) is important for renal salt handling and blood-pressure homeostasis. The canonical NCC-activating pathway consists of With-No-Lysine (WNK) kinases and their downstream effector kinases SPAK and OSR1, which phosphorylate NCC directly. The upstream mechanisms that connect physiological stimuli to this system remain obscure. Here, we have shown that aldosterone activates SPAK/OSR1 via WNK1. We identified 2 alternatively spliced exons embedded within a proline-rich region of WNK1 that contain PY motifs, which bind the E3 ubiquitin ligase NEDD4-2. PY motif-containing WNK1 isoforms were expressed in human kidney, and these isoforms were efficiently degraded by the ubiquitin proteasome system, an effect reversed by the aldosterone-induced kinase SGK1. In gene-edited cells, WNK1 deficiency negated regulatory effects of NEDD4-2 and SGK1 on NCC, suggesting that WNK1 mediates aldosterone-dependent activity of the WNK/SPAK/OSR1 pathway. Aldosterone infusion increased proline-rich WNK1 isoform abundance in WT mice but did not alter WNK1 abundance in hypertensive Nedd4-2 KO mice, which exhibit high baseline WNK1 and SPAK/OSR1 activity toward NCC. Conversely, hypotensive Sgk1 KO mice exhibited low WNK1 expression and activity. Together, our findings indicate that the proline-rich exons are modular cassettes that convert WNK1 into a NEDD4-2 substrate, thereby linking aldosterone and other NEDD4-2-suppressing antinatriuretic hormones to NCC phosphorylation status.
Li H, Satriano J, Thomas JL, Miyamoto S, Sharma K, Pastor-Soler NM, Hallows KR, Singh P: Interactions between HIF-1α and AMPK in the regulation of cellular hypoxia adaptation in chronic kidney disease. Am. J. Physiol. Renal Physiol. 309: F414-F428, 2015.
Renal hypoxia contributes to chronic kidney disease (CKD) progression, as validated in experimental and human CKD. In the early stages, increased oxygen consumption causes oxygen demand/supply mismatch, leading to hypoxia. Hence, early targeting of the determinants and regulators of oxygen consumption in CKD may alter the disease course before permanent damage ensues. Here, we focus on hypoxia inducible factor-1α (HIF-1α) and AMP-activated protein kinase (AMPK) and on the mechanisms by which they may facilitate cellular hypoxia adaptation. We found that HIF-1α activation in the subtotal nephrectomy (STN) model of CKD limits protein synthesis, inhibits apoptosis, and activates autophagy, presumably for improved cell survival. AMPK activation was diminished in the STN kidney and was remarkably restored by HIF-1α activation, demonstrating a novel role for HIF-1α in the regulation of AMPK activity. We also investigated the independent and combined effects of HIF-1α and AMPK on cell survival and death pathways by utilizing pharmacological and knockdown approaches in cell culture models. We found that the effect of HIF-1α activation on autophagy is independent of AMPK, but on apoptosis it is partially AMPK dependent. The effects of HIF-1α and AMPK activation on inhibiting protein synthesis via the mTOR pathway appear to be additive. These various effects were also observed under hypoxic conditions. In conclusion, HIF-1α and AMPK appear to be linked at a molecular level and may act as components of a concerted cellular response to hypoxic stress in the pathophysiology of CKD.
Roy A, Al-bataineh MM, Pastor-Soler NM: Collecting duct intercalated cell function and regulation. Clin J Am Soc Nephrol 10:305-324, 2015.
Intercalated cells are kidney tubule epithelial cells with important roles in the regulation of acid-base homeostasis. However, in recent years the understanding of the function of the intercalated cell has become greatly enhanced and has shaped a new model for how the distal segments of the kidney tubule integrate salt and water reabsorption, potassium homeostasis, and acid-base status. These cells appear in the late distal convoluted tubule or in the connecting segment, depending on the species. They are most abundant in the collecting duct, where they can be detected all the way from the cortex to the initial part of the inner medulla. Intercalated cells are interspersed among the more numerous segment-specific principal cells. There are three types of intercalated cells, each having distinct structures and expressing different ensembles of transport proteins that translate into very different functions in the processing of the urine. This review includes recent findings on how intercalated cells regulate their intracellular milieu and contribute to acid-base regulation and sodium, chloride, and potassium homeostasis, thus highlighting their potential role as targets for the treatment of hypertension. Their novel regulation by paracrine signals in the collecting duct is also discussed. Finally, this article addresses their role as part of the innate immune system of the kidney tubule.
Campese VM, Lakdawala R: The Challenges of Blood Pressure Control in Dialysis Patients. Recent Pat Cardiovasc Drug Discov 10:34-59, 2015.
Hypertension is very prevalent among patients with chronic kidney disease (CKD) and end-stage kidney disease (ESRD). However, there are still several unsolved issues pertaining to the definition, variability, diagnosis and management of hypertension in these patients. This manuscript critically reviews the current challenges in clinical practice in defining, diagnosing and treating hypertension in CKD and ESRD patients. Moreover, the manuscript reviews the pharmacokinetics, pharmacodynamics and safety of most anti-hypertensive drugs used in the management of these patients.
Fong M, Shavelle D, Weaver FA, Nadim MK: Renal denervation in heart failure. Current Hypertension Reports 17: 17, 2015.
Heart failure has emerged as one of the most important diseases of the past century. The understanding and treatment of heart failure has evolved significantly over the years. As we move further into the era of device therapy, attention has turned to the idea of sympathetic nervous system modulation through renal denervation to treat heart failure. In this review, we summarize the background research, denervation technique, and current studies on renal denervation for the treatment of heart failure. We also compare and contrast the work on carotid barostimulation.
Shah N, Meouchy J, Qazi Y: Bortezomib in kidney transplantation. Curr Opin Organ Transplant 20:652-656, 2015.
PURPOSE OF REVIEW:
The purpose of this review is to evaluate the effectiveness of bortezomib in the recent literature for the prevention and treatment of kidney transplant rejection.
Several studies have analyzed bortezomib alone and in comparison to more traditional immunosuppressive agents during the last 2 years. If administered prior to transplant or soon thereafter, bortezomib appears to lower donor-specific antibody levels and improves graft survival. Its role as a treatment option for antibody-mediated rejection after transplant remains unclear, with limited evidence supporting its long-term success.
Bortezomib appears to be a promising early desensitizing agent in the world of kidney transplantation and high short-term success rates have been observed. However, additional randomized trials would be useful to more conclusively demonstrate its effectiveness and optimal administration time in relation to transplant surgery.
Matsuoka L, Alicuben E, Woo K, Cao S, Groshen S, Qazi Y, Smogorzewski M, Selby R, Alexopoulos S: Kidney transplantation in the Hispanic population. Clin Transplant (in press), 2015.
Hispanic race and low socioeconomic status are established predictors of disparity in access to kidney transplantation. This single-center retrospective review was undertaken to determine whether Hispanic race predicted kidney transplant outcomes. A total of 720 patients underwent kidney transplantation from January 1, 2004 to December 31, 2013, including 398 Hispanic patients and 322 non-Hispanic patients. Hispanic patients were significantly younger (p < 0.0001), on hemodialysis for longer (p = 0.0018), had a greater percentage with public insurance (p < 0.0001), more commonly had diabetes as the cause of end-stage renal disease (p = 0.0167), and had a lower percentage of living donors (p = 0.0013) compared to non-Hispanic patients. There was no difference in one-, five-, and 10-yr graft (97%, 81%, and 61% vs. 95%, 76%, and 42% p = 0.18) or patient survival (98%, 90%, and 84% vs. 97%, 87%, and 69% p = 0.11) between the Hispanic and non-Hispanic recipients. Multivariate analysis identified increased recipient age and kidney donor profile index to be predictive of lower graft survival and increasing recipient age to be predictive of lower patient survival. In the largest single-center study on kidney transplantation outcomes in Hispanic patients, there is no difference in graft and recipient survival between Hispanic and non-Hispanic kidney transplant patients, and in multivariate analysis, Hispanic race is not a risk factor for graft or patient survival.
Honors & Awards
Kenneth R. Hallows, MD, PhD, FASN
- Baltimore PKD Core Center Pilot Grant Award
- U.S. Department of Defense Investigator-Initiated Research Award
- U.S. Department of Defense Clinical Trial Award
- NIH R01 DK075048 Grant Award
Mitra K. Nadim, MD
- Faculty Teaching Award, Keck School of Medicine
Nuria M. Pastor-Soler, MD, PhD, FASN
- Wright Foundation Pilot Grant Award